Process for producing acrylonitrile polymer fiber of predetermined fiber color



United States Patent 3,383,350 PROCESS FOR PRODUCING ACRYLONITRILEPOLYMER FIBER OF PREDETERMINED FI- BER COLOR Bobby M. Pettyjohn, Camden,S.C., assignor to E. I. du Pont de Nemours and Company, Wilmington,Del., a corporation of Delaware No Drawing. Continuation-impart ofapplication Ser. No. 261,871, Feb. 28, 1963. This application Dec. 9,1965, Ser. No. 512,812

4 Claims. (Cl. 26032.6)

This is a continuation-in-part of Ser. No. 261,871, filed Feb. 28, 1963,now abandoned.

This invention relates to production of acrylic fibers of improved coloruniformity, and more particularly to the control of fiber yellownesswithin narrow limits.

It is well-recognized that acrylic fibers tend to discolor on exposureto high temperature or alkali to give a somewhat yellowish product.While it would be desirable to provide a fiber which has no off-whiteshading and excellent reflectance, particularly in the interest offlexibility in end uses and good clarity of dyeings, this ideal has notyet been attained. As a reasonable compromise, fiber proc essors arewilling to accept maintenance of a relatively uniform degree ofwhiteness so that lot-to-lot variations in whiteness do not presentproblems in duplication of dye shades or in variable response tobleaching and other finishing steps. In endeavoring to get uniformcoloration, it it has been necessary to use combinations of additives inthe spinning solutions as well as various polymer and fiberafter-treatments. Using previously known processes and additives, thedetermination and acceptable control of fiber coloration, particularlyduring continuous process production, has not been attainable. Moreover,certain treatments which initially reduce coloration actually promotethe development of color during subsequent processing such as scouring,washing etc.

It is, therefore, an object of the present invention to provide aprocess for preparing acrylic fibers having uniform coloration. It isanother object of this invention to provide a process for continuouslycontrolling coloration during the spinning process. It is a furtherobject to provide a process for improving the whiteness of acrylicfibers which does not adversely affect other fiber properties and doesnot promote formation of color during subsequent processing.

It has now been discovered, and it is on this discovery that theinvention is in large part predicated, that predetermined and uniformcoloration of acrylic fibers can be attained with a procedure involvingmonitoring of the color of the spinning solution from which the fibersare spun and treating the solvent to be used to make additional spinningsolution in response to the monitoring information obtained. Moreparticularly, the objects of this invention are accomplished bydissolving an acrylonitrile polymer in N,N-dimethylformamide (DMF) toform a spinning solution, monitoring the resulting solution to determineits coloration, and thereafter adding to the N,N- dimethylformamideprior to dissolution of polymer therein a controlled amount of citricacid (CA) or diethylenetriarninepentaacetic acid (DTPA) to reduce thecoloration of solution prepared to a predetermined level. The additionto N,N-dimethylformamide of very small amounts of either of theforegoing acids, i.e., from about 25 to about 800 parts per millionbased on the weight of polymer to be dissolved therein, is effective inreducing coloration potential With an almost immediate gain in thewhiteness of the spinning solution being produced in a continuousprocess and of the fibers formed therefrom. In view of the rapid andefiicient action of these acids used in accordance with the foregoingdiscovery, it is now possible rapidly to attain a good coloration levelin the continuous production of acrylic fiber. Where there is anextended lapse of time between the preparation and the spinning of thesolution, additional protection may be obtained by addition of CA orDTPA to the solution, but this procedure is less desirable sinceyellowness already developed prior to this later addition is noteliminated. Monitoring of the solution just prior to spinning ispreferred to monitoring of fiber whiteness, due to the early indicationof trends afforded thereby. For example, commonly 48 hours separate theperiod in which polymer is first dissolved to initiate the process andthe time when product therefrom is obtained and its color determined.With such lags great variation in product would result from changesbased on the product color alone.

In carrying out the process of this invention, the determination ofcoloration can be made by using a differential colorimeter. The spinningsolution may be monitored at selected time intervals or monitoredcontinuously using apparatus of the type described in McKinney et al.US. 3,020,795. However monitored, the information obtained is used toindicate an initial addition of acid, a continued addition or adiminishng of acid added, all within the acid range given hereinbefore.Generally amounts of ether CA or DTPA greater than 800 parts per millionare not required to maintain the predetermined color level. Theparticular amount required will vary depending on such factors as thesolution temperatures employed, composition of the spinning solution,and the rate of extrusion and denier of the acrylonitrile polymer fibersformed.

The term acrylonitrile polymer as used herein is meant to include ahomopolymer of acrylonitrile as well as such copolymers as thosecontaining at least of acrylonitrile and up to 15% of one or moremonoethylenically unsaturated monomers copolymerizable withacrylonitrile. Preparation of these polymers is well known, suchprocesses being disclosed in US. Patents 2,486,241, 2,456,238,2,837,500, and 2,837,501 as well as others.

In the examples which follow, the color value b is determined using themethod described in the Journal of the Optical Society of America, vol.42, No. 9 (1952), pages 652 to 666, by L. G. Glasser and D. J. Troy. Theb values reported are proportional to the sample yellowness and aredetermined by reflectance of filtered light from the sample. Inmeasuring the solution color, samples are taken at timed intervals andpoured into a flat-bottom dish which is placed over one window of thedifferential colorimeter, the standard reference plate being placed overthe other window. In making continuous measurements of the solutioncolor, the window of the apparatus described in McKinney et al. mayserve as one window of the differential colorimeter. Fiber samples areprepared for color value measurement by chopping to about 0.06 inch(0.16 cm.) or shorter lengths, slurrying in water, filtering the slurryto form a pad and drying at room temperature until dry to the touch. Thepad is then placed on one window of the differential colorimeter withthe standard reference plate being placed on the other window. Readingsare taken with the pad oriented in each of two directions, the onedirection being at 90 relative to the other.

The following examples in which parts and percentages are by weightunless otherwise specified further illustrate the invention.

EXAMPLE 1 A. Spinning solution is prepared to contain 30% by weight of aterpolymer consisting essentially of 93.6% acrylonitrile, 6% methylacrylate, and 0.4% sodium styrenesulfonate in N,N-dimethylformamide(DMF), and 0.4% TiO based on polymer, is added as a delusterant. Thesolution is continuously dry-spun to a multifilament yarn which, aftersimultaneous drawing 4.54X (to 454% of its spun length) and extractionin a water bath maintained near its boiling point, has adenier-per-filament of 4.5.

BE. Subsequent solutions are prepared in accordance with Part A exceptthat DTPA in increasing amounts is added, as a 17.5% dispersion in DMF,to the DMF prior to addition of the polymer. The successive solutionsare spun continuously and the product fiber representative of each isanalyzed for yellowness. Results are summarized in Table l.

This example illustrates yellowness regulation by the process of thisinvention as applied to the continuous production of 6.0 d.p.f. acrylictow. Diethylenetriaminepentaacetic acid in amounts specified, based onpolymer to be added, is added to the DMF as a 17.5% dispersion in DMFprior to addition of the polymer.

In this example, product yellowness changes are used as the basis forchange in the amount of DTPA added. A substantial periol of time elapsesbetween changes in solution and the recognition of the result in theproduct fiber. This lagtime is taken into account to avoidover-correction." The following directives are adopted:

(1) When one 3-point running average value of solution yellownessdeviates more than 1.1 b from the aim, change DTPA by 100 ppm.

(2) When three consecutive 3-point running average values of solutionyellowness deviate from 0.6 to 1.0 b from the aim, change DTPA by 50ppm.

(3) When eight consecutive 3-point running average values of solutionyellowness are on one side of but deviate from the aim by less than 0.6b, change DTPA by 50 ppm.

In all cases, high yellowness calls for an increase in DTPA, and lowyellowness calls for a decrease in DTPA. It is further directed for thisexampe that a maximum of ppm. of DTPA may be used. By 3-point runningaverage is meant that each value recorded is the average of threesuccessive determinations, the latest result being averaged with the twovalues just preceding it.

It has been found that solution color correlates well with final productcolor if all process aspects other than solution color are preciselymaintained constant. While for any short period of time such precisecontrol may be maintained, it has been found that provision must be madefor compensating adventitious variations in other conditions which willaffect this correlation. The following empirically derived relationshipprovides for a running adjustment in solution yellowness aim:

This equation states that the aim solution yellowness (SY) for theensuing period is calculated as that experienced for the previous periodless twice the difierence between the product yellowness (PY) observedduring the previous eriod and the product yellowness aim.

Tables 2 and 3 are records of two periods of continuous spinning of 6.0d.p.f. acrylic tow using the present discovery and will illustrate theutility of the novel process of this invention. The product yellownessaim in these cases is 2.0.

The method of yellowness regulation employed in this example is betterunderstood by considering the times when data become available.Reference is made to the first 5 days of test, summarized in Table 2, asan illustration.

The six 3-point running average values of solution b listed opposite Dayof Test 1 are available for averaging by about 6 a.m. of that day. Dueto the lagtime, however, these values are pertinent to productyellowness values appearing on the third day of test. The product coloraverage for that day is calculated about noon, and the two values,solution color 5.7 and product yellowness 1.9, are employed to calculatea new solution color aim (5.9) according to the preceding formula. Itwill be noted that this aim is higher than at least eight 3-pointrunning average solution [1 values reading backwards from the latestvalue available at that time (4.8 obtained at 12 n. on Day of Test 3).No DTPA was being used at that time, however, so no change is possibleunder the operating directives established.

On the fourth day of test, a new solution color aim, 5.0, is availablebased on the product color available about noon and the average solutioncolors of the second day of test. It will be noted that the four latestsolution color b values at that time are above the aim. By approximately6 a.m. that day, four additional values have been accumulated which alsoare above the aim. Proper adherence to procedure would have led to achange (to add 50 ppm. DTPA) at 8 a.m. on the fifth day of test. Theaddition was not begun, however, until about 4 pm. That was late, butotherwise in accordance with the operating instructions. In this generalmanner the data for the remaining 26 days of operation (Tables 2 and 3)were obtained and employed in accordance with the present discovery.

Despite the variations from proper procedure as noted under Remarks inTable 2 and 3, study of the product color data show satisfactorycontrol. These results are particularly significant if it is realizedthat the changes made to bring about a product color of a particularvalue, are made in point of time about two days in advance of theexistence of the product in form suitable to determine its color. Hencethe method of the invention is of effective control in continuousoperations.

As noted above citric acid can be used in place of the DTPA in likemanner with similar results and this is shown in the following example.

EXAMPLE 3 TABLE 4 Additive None 50 p.p.m. DTPA 50 ppm. citric acid 4.84.2 4.2 1.8 1.5 1.8 2.76 2.88 2. 66 Elongation, perce 30.9 31.6 32. 5

B. In a further test of the effectiveness of citric acid in reduction ofrate of yellowness development several solutions are prepared in thelaboratory to contain 10% by weight of a polymer similar to thatemployed in Example 1. The DMF employed as solvent in each case isrepresentative of one of four lots known to have differing propensitiesfor yellowing polymer dissolved and heated therein. Before addition ofthe polymer, the amount of citric acid indicated in Table 5 is added tothe solvent. The citric acid added to the solvent is based on the weightof polymer to be added. No delusterant is added.

The solutions prepared are stored for three hours at 65 C., which heattreatment has been found to approximate the amount of thermaldiscoloration reached in a commercial spinning process. The solutionsare poured into a spectrophotometer cell which provides a 1-cm.thickness of solution in the path of the beam and the absorbance ismeasure at 345 my using pure solvent as a standard. The results aretabulated in Table 5. It will be noted that a leveling effect isattained, the larger reductions generally occurring with those lots ofsolvent which have the greater tendency to promote yellowness in thepolymer.

TABLE 5 DMF Lot N o. Citric Acid, Absorbance, Approx. Final p.p.m. 345 mProduct [1" It will be readily apparent from the foregoing examples thatthe broadest utility of the present invention is realized by determiningthe final product-color in advance of spinning. By utilizing the processof this invention, corrections are made based on the yellowness of thespinning solution, and thus the yellowness of the resulting fiber ismaintained at a predetermined, more-uniform level. As previouslyindicated, a useful prediction of final product color can be made bydetermining the whiteness of the solution removed from the deliverysystem in advance of, but adjacent to, the spinning head. Thestatistical data thus obtained are utilized in determining routineoperating procedures to be applied to specific operating conditions.While direct monitoring of the supply of solution passing through thedelivery system is preferred, it will be apparent that the advantages ofthis invention may be obtained by utilizing similar conditions andequipment in laboratory apparatus to estimate the color of the solutionas samples from the delivery system. Thus, a change which affects thelevel of whiteness can be predicted and compensated for before it isseriously apparent in the final product.

The process of this invention is, of course, not limited to utilizingsolutions prepared from the polymer specifically described in theexamples, but is equally applicable to other polymers containing atleast combined acrylonit-rile in the polymer chain. Copolymerscontaining up to 15% of monomers of monoethylenically unsaturatedcopolymerizable monomers such as those described in US. 2,436,926 andUS. 2,743,944 are suitable. Among those monomers are methylmethacrylate, ethyl methacrylate, butyl methacrylate, octylmethacrylate, 2-nitro-2-methyl propyl methacrylate, methoxyethylmethacrylate, chloroethyl methacrylate, phenyl methacrylate, cyclohexylmethacrylate, dimethyl aminoethyl methacrylate, and the correspondingesters of acrylic or alpha-chloroacrylic acids; acrylandmethacryl-amides or monoalkyl substitution products thereof; unsaturatedketones such as methyl vinyl ketone, phenyl vinyl ketone, and methylisopropenyl ketone, vinylidene chloride, vinyl chloride, vinyl fluoride,vinyl carboxylates such as vinyl acetate, vinyl chloroacetate, vinylpropionate, vinyl butyrate, vinyl benzoate, vinyl thiolacetate, andvinyl stearate, esters of fumaric maleic, citraconic, and mesaconicacids, N- alkyl maleimides; N-vinyl carbazole, N-vinyl succ-inirnide,N-vinyl phthalimide, vinyl esters, mono-olefins, or substitutionproducts thereof such as styrene, furyl ethylene, ethylene, andisobutylene may be used. In addition, the copolymers may contain fromabout 0.1% to about 10% of a copolymerizable monomer having sulfonicacid or sulfonate salt groups such as allyloxyethylsulfonic acid,allylthiopropanolsulfonic acid, vinyldichlorobenzenesulfonic acid,naphthylethylene sulfonic acid, methyl styrenesulfonic acid, as well asdisulfonic and amino sulfonic acids.

The concentration of the polymer in the spinning solution should bebetween about 25% and 40%, and the solution should have a viscositywithin the range of about 15 to 750 poises at the temperature ofspinning with viscosities between about 50 and about 200 poises beingpreferred. Spinning of the polymers to form fibers may be accomplishedusing known dryand wet-spinning procedures.

In preparing the polymers and spinning solutions, various additives suchas flame retardants, pigments, antistatic agents and spinning adjuvantsmay be included. The adjuvants, such as flame retardants, may beincluded in amounts up to about 10% by weight of the polymer withoutinfluencing adversely the degree of whiteness regulation afforded bythis invention.

It will be appreciated that changes from the details given can be madein this invention without departing from its scope.

What is claimed is:

1. In the continuous production of acrylic polymer filaments in whichacrylic polymer is dissolved in a solvent to provide a spinning solutionand the resulting spinning solution is extruded in a spinning zone toform acrylic filaments which are processed to produce an acrylic fiberform and the color of the filaments determined, that method of adjustingthe color of the acrylic fiber being produced comprisingsa-mplingspinning solution as it is advanced to the spinning zone and analyzingits color, and adding to the solvent to make additional spinningsolution prior to the addition thereof to the previously formed spinningsolution, an effective amount of diethylenetriaminepentaacetic acid toreduce the coloration of spinning solution produced thereby to a levelto produce fibers of satisfactory color.

2. The process of claim 1 in which the acid is added in an amount of 25to 800 parts per million based on polymer to be added.

3. The process of claim 2 in which the polymer comprises at least 85%acrylonitrile and up to 15% of a monoethylenically unsaturated monomercopolymerizable with acrylonitrile and the solvent isN,N-dimethylformamide.

4. The process of claim 1 further comprising analyz- References CitedUNITED STATES PATENTS 2,502,030 3/1950 Scheiderbauer 26029.1 2,878,2063/1959 Holmes et al 260-32.6 3,150,160 9/1964 Dexter 260-439 MORRISLIEBMAN, Primary Examiner.

H. S. KAPLAN, J. A. GAZEWOOD,

Assistant Examiners.

1. IN THE CONTINUOUS PRODUCTION OF ACRYLIC POLYMER FILAMENTS IN WHICHACRYLIC POLYMER IS DOSSOLVED IN A SOLVENT TO PROVIDE A SPINNING SOLUTIONAND THE RESULTING SPINNING SOLUTIO IS EXTRUDED IN A SPINNING ZONE TOFORM ACRYLIC FILAMENTS WHICH ARE PROCESSED TO PRODUCE AN ACRYLIC FIBERFORM AND THE COLOR OF THE FILAMENTS DETERMINED, THAT METHOD OF ADJUSTINGTHE COLOR OF THE ACRYLIC FIBER BEING PRODUCED COMPRISING SAMPLINGSPINNING SOLUTION AS IT IS ADVANCED TO THE SPINNING ZONE AND ANALYZINGITS COLOR, AND ADDING TO THE SOLVENT TO MAKE ADDITIONAL SPINNINGSOLUTION PRIOR TO THE ADDITION THEREOF TO THE PREVIOUSLY FORMED SPINNIGSOLUTION, AN EFFECTIVE AMOUNT OF DITHYLENETRIAMINEPENTAACETIC ACID TOREDUCE THE COLORATION OF SPINNING SOLUTION PRODUCED THEREBY TO A LEVELTO PRODUCE FIBERS OF SATISFACTORY COLOR.